I suppose we all loved those kind of sci-fi movies where terrible things came out of swamps and came to Mars. And there's usually some poor girl. All the guys are trying to desperately handle levers and saying, go to something or other.
When I am seriously composing, sometimes a phrase will come into my head, a catch phrase. When I was writing pop songs for a few years, as a career, separate from my folksinging career, I used to write songs for pop singers.